Orthodontic materials

GOOD MORNINGOrthodontic materials

Presented byDr Isha SharmaP.G Ist year

CONTENTS

INTRODUCTION ORTHODONTIC BRACKETS IMPRESSION MATERIALS GYPSUM PRODUCTS DENTAL CEMENTS USED IN ORTHODONTICS ORTHODONTIC ADHESIVES AND RESINS ELASTOMERIC LIGATURES AND CHAINSACRYLIC RESINREFERENCES Introduction The rapid advancement seen in the field of orthodontics has been primarily due to improvement in the field of material sciences.

The better understanding of biologic problems and advancement in orthodontic materials has lead to improved appliance design and treatment strategies. Classification of orthodontic MaterialsArch wire materialsBracket and attachment materialsAuxiliary force delivery systemImpression materialsLuting materialsSealents and adhesion promotersEtching /conditioning and crystal growth systemsBonding materials BRACKETS7EVOLUTION OF BRACKETSBandelette plates-by Pierre Fauchard.. They are crude metal plates that were ligated to the teeth with brass or silver ligature wire.In the late 1900s, found out if a rigid framework is tied to teeth, the arch could be expanded as dictated by the appliance

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THE E-ARCH APPLIANCE (1900)The first fixed appliance designed by AngleUsed for tipping teeth into new aligned positionUsed stationary anchorageExpanded the arch-traction screwNo individual tooth control possible

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PIN AND TUBE APPLIANCE(1910) E.H.ANGLE

Most of the teeth were banded .Vertical tubes were soldered to the bands with their long axis parallel to the long axis of the crown. Rotational movements were difficult to obtain .

10RIBBON ARCH APPLIANCE (1915)

The first bracket devised in 1915 by angleBig step in evolution of bracketsRotational movementsBucco-lingual and inciso-gingival movementsDistal Tipping Of Buccal Segment not possibleMesiodistal axial movement not possibleArch wire didnt provide stabilizationBracket and attachment materialsBracket It is precisely fabricated orthodontic attachment made of metal ,plastic or ceramic material,which can be bonded to a tooth or welded to a band.It carry a horizontal or vertical channel of standard size called a slot.The base of the bracket usually contains a welded mesh or other retentive structures to increase bond stength.(Glossory of orthodontic terms)The term is used only when referring to those devices that are open in one side -vertical or horizontal

The term bracket came to be in use in orthodontics when Dr. Angle introduced the ribbon arch appliance

13BASED ON MATERIALSA) METAL BRACKETS 1) Stainless steel brackets 2) Gold-coated brackets 3) Platinum-coated brackets 4) Titanium bracketsB) PLASTIC BRACKETS 1) Polycarbonate brackets 2) Polyurethane-composite brackets 3) Thermoplastic-polyurethane brackets C) CERAMIC BRACKETS 1) Monocrystalline alumina 2) Polycrystalline alumina 3) Polycrystalline Zirconia Metal bracketsMetal brackets rely on mechanical retention for bonding and mesh gauze is the conventional method of providing retention.The use of small less noticeable metal bases help to avoid gingival irritation.Corrosion of metal brackets may be a problem and black and green stain have appeared with bonded stainless steel attachment.

Crevice corrosion of metal arising in areas of poor bonding may result from type of stainless steel used.

16STAINLESS STEEL BRACKETS Brackets made of stainless steel are alloys formulated according to the American Iron and Steel Institute (AISI) in the austenitic classes 303, 304, 316, and 317.

According to this classification, as the number increases, more alloying metals are added to the iron, while its carbon content is lowered. STAINLESS STEEL COMPOSITION AND STRUCTURE

The steels, which have AISI numbers beginning with the numeral 3, are all austenitic; the higher the number, the less non-ferrous the alloy. The letter L signifies lower carbon content. 303 has 17-19% Cr, 8-10% Ni and 0.6% Mo 316 has 16-18% Cr, 10-14%Ni, 2% Mn and 0.08% C 316L has 16-18% Cr, 10-14% Ni, 2.5% Mo and0.02% C SAF 2205 has 22% Cr, 5.5% Ni, 3% Mn, and 0.03% C

The 2205 stainless steel alloy has a duplex microstructure consisting of austenitic and delta-ferritic phases and is harder and demonstrated less crevice corrosion than 316L alloy. (Oshida & Moore)19Steels with a lower AISI number starting with 3 are rather soft and easier to mill, but their corrosion resistance is low

Relatively high Chromium content in SS favours the stability of BCC unit cells of ferrite.

Ni, Cu, Mn favours an FCC structure of austenite

Other additives are,Silicon (Si) if kept at lower concentration, improves resistance to oxidation and carburization at higher temperatures & to corrosion

Sulfur (S) 0.015% sulfur content allows easy machining of wrought partsPhosphorus (P) allows use of a lower temperature for sinteringManganese (Mn) used as a replacement for nickel to stabilize austenite

Gold-plated stainless steelbracesThese braces are often employed for patients allergic to nickel (a basic and important component of stainless steel), but may also be chosen because some people simply prefer the look of gold over the traditional silver-coloured braces.

PLATINUM COATED BRACKETS

Five times the abrasion resistance of gold.

A smoother, harder surface than stainless steel

For reduced friction and improved sliding mechanics is achieved.

TITANIUM BRACKETS

It is the latest metal to be used for the manufacture of brackets.

It is more biocompatable and allows superior finish there by decreasing friction.

They are ideal for use in patient with nickel hypersensitivity.

Low thermal conductivityIncreased retention rough surface

Single piece- no soldering joints- nickel free

Corrosion resistant

They are more expensive than stainless steel brackets.

26NICKEL-FREE BRACKETSLaser structured bracket base for retention

Made of Cobalt chromium (CoCr) dental alloy

One-piece construction (without solder) by metal injection molding technique

Laser structured bracket base for retention

Plastic brackets Cohen and Silverman (IPB brackets) manufactured by GAC in 1963.

Plastic attachment are made of polycarbonate and are used mainly for esthetic reason.Pure plastic brackets lack strength to resist distortion and breakage,wire slot wear [which leads to loss of tooth control],uptake of water,discoloration,and need for compatible bonding resinSuch plastic brackets may be usefull in minimal force situation and for treatment for short duration ,particularly in adults.

29DISADVANTAGES OF POLYCARBONATE BRACKETS

Polycarbonate brackets undergo creep deformation when transferring torque loads generated by arch wires to teeth. Discoloration of first generation unfilled polycarbonate brackets during clinical aging. They absorb water to a slight extent and tend to weaken in the course of about one year.

Various reinforced polycarbonate brackets were, Polymer fiber reinforced Fiberglass reinforcedCeramic reinforcedMetal slot reinforcedMetal slot and ceramic reinforced

CERAMIC BRACKETSCeramic orthodontic brackets are machined from monocrystalline or polycrystalline aluminium oxide.

Such bracket should combine the estheics of plastic and the reliability of metal brackets

Ceramic brackets bond to enamel by two different mechanism:

Mechanical retention via indentation and undercut in the baseChemical bonding by means of a silane coupling agent.TYPES OF CERAMIC BRACKETS

Monocrystalline (Sapphire)Polycrystalline AluminaPolycrystalline Zirconia-Yttrium oxidePartially Stabilised Zirconia

MANUFACTURING METHODS FOR CERAMIC BRACKETSMONOCRYSTALLINE (SAPPHIRE) BRACKETS

The first step in the manufacture of the single-crystal brackets is the slow cooling of the molten high-purity aluminium oxide under controlled conditions from temperatures above 2100C.

The resulting bulk single crystal alumina rod or bar form is then milled into brackets using diamond cutting, Nd: YAG lasers, or ultrasonic cutting.

The single-crystal brackets are also subsequently heat treated to remove surface imperfections and stresses created by the milling process.

36POLYCRYSTALLINE ALUMINA BRACKETS

These brackets are manufactured by first combining a suitable binder with aluminium oxide particles (average of 0.3m size) so that this mixture can be molded into the shape of a bracket.

This molded mixture is then heated (fired) at temperatures in excess of 1800C to burn out the binder and achieve sintering of the particles.

37 Diamond cutting tools are then used to machine the slot dimensions.

Heat treatment is subsequently performed to relieve the stresses caused by the cutting and to remove surface imperfections resulting from the manufacturing processes. Structural imperfections at the grain boundaries or trace amounts of sintering aids can serve as sites of crack initiation under stress.

POLYCRYSTALLINE ZIRCONIA BRACKETS The polycrystalline zirconia brackets are manufactured by impression molding, followed by hot isostatic pressing. Yttrium oxide-partially stabilized zirconia (YPSZ) can be obtained in bulk form by sintering (without pressure up to 95% of the theoretical density) a mixture of ultrafine powder (average starting particle size of 0.2m) and 5wt% Yttrium oxide.A polycrystalline microstructure with an average grain size of about 0.5m is obtained, and hot isostatic pressing is subsequently employed to remove residual porosity with limited additional grain growth

40COMMERCIALLY AVAILABLE CERAMIC BRACKETSMONOCRYSTALLINE ALUMINAInspireStarfire TMBPOLYCRYSTALLINE ALUMINA1) Allure 7) Mxi2) Clarity 8) Signature3) Fascination9) Virage4) Intrigue10) CeramaFlex (with polycarbonate base)5) 20/2011) InVu6) Lumina

POLYCRYSTALLINE ZIRCONIA1) Hi-Brace41MXi (TP ORTHODONTICS)

POLYCRYSTALLINE ALUMINA CERAMIC BRACKETSMONOCRYSTALLINE CERAMIC BRACKETInspire

Starfire42POLYCRYSTALLINE ALUMINA CERAMIC BRACKETSAllure (GAC)

CLARITY (3M UNITEK)

Micro-crystalline bonding surface

20/40 (American Orthodontics)

43Metal-Reinforced Ceramic Brackets

Clarity These are in vogue because of their possible reduction in enamel damage during debonding.

The bracket with metal {stainless steel} slot also decrease the friction values which are comparable to other stainless steel brackets.

IMPRESSION MATERIALS DEFINITIONAny substance or combination of substance used for making an impression or negative reproduction. GPT-8

Materials used to produce accurate replicas should fulfill the following criteria to obtain an accurate impression- They should be fluid enough to adapt to the oral tissue.Should be viscous enough to be contained in the tray that is seated in the mouth.They should transform into rubbery or rigid solid in the mouth.

Ideally total setting time should be less than 7 mins.

The set impression should not distort or tear when removed from mouth.

Impression made from these material should be dimensionally stable.

Should be biocompatible.

AlginateAlgin - a peculiar mucous extract yielded by Algae (brown seaweed).

Algin linear polymer with numerous carboxylic acid groups named it as anhydro beta - manuronic acid ( alginic acid ).

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Alginic acid is a copolymer of anhydro - beta D mannuronic acid & anhydro - beta - d guluronic acid.

In England, 40 yrs later, S. William Wilding received the patent for alginate as impression material.CompositionPotassium alginateHydro gel formerTo dissolve in water and react with calcium ion 15 18 g %Calcium sulphate dihydrateProvides Ca ions & react with potassium alginate to form insoluble calcium alginate gel14 16 g %Potassium sulphates , potassium zinc fluoride , potassium titanium fluoride , silicates or boratesAccelaratorCounteract the inhibiting effect of hydro colloid gels on setting of gypsum and give high quality surface to dies3 10 g %Sodium phosphatesRetarderReact with preferentially with Ca ions to provide working time before gelation2 g %Diatomaceous earth or silicate powderControls the consistency of the mixed alginate & flexibility of set material56 60 g %Organic glycolsMake the powder dustlesssmallWinter green and peppermint , aniseTo produce a pleasant tasteTracePigments To provide coloursTrace Disinfectants (quaternary ammonium salts & chlorhexidine )To help in disinfection of viable organism 1 2 g %Sodium silico fluorideControls the pH4 g %Zinc oxideAct as a filler & has some influence on the setting time & physical properties of gel4 g %SETTING REACTION: SOL GEL reactioni) 2 Na3 PO4 + 3 Ca SO4 Ca3 (PO4)2 + 3 Na2 SO4(Sodium phosphate) (Calcium sulphate) (Retarder) (Reactor)

ii) Sodium Alginate + Ca SO4 + H2O Ca Alginate + Na2 SO4 (Powder) (Reactor) (Gel)Two main reactions occurs during setting:Properties:StrengthTime dependent.Greater at higher rate of loading. (Impression to be removed with a Snap)Compressive strength: 5000 to 9000 g/cm2Tear strength : 380 to 700 g/cm2

Factors affecting strength:Water/Powder ratio-too much or little water reduces gel strengthMixing time.-over and under mixing reduce strength

FlexibilityIt is about 11-15% at a stress of 1000gm/cm2Some of the hard set material have lower values{3-8%}Lower water-powder ratio Lower flexibility.

Permanent Deformation (1.2%)Reduced by bulk of material. (5mm between tray and tissues)

Manipulation:DispensingMixingLoading the trayPerforated tray.Rim lock trays.Wisp of cotton wool secured to the tray.Adhesives: Methylcellulose.Taking Impression

Dimensional stabilityIn air loss of water shrinks.In water absorbs water swells.Storage: in 100% relative humidity for 1 hr.Should be poured immediately.

Shelf lifeDeteriorates at elevated temp.

Agar( elastic reversible hydrocolloids )Introduced by Alphous poller of Vienna in 1925 & Adopted commercially as Dentacol in 1928

It was the first successful elastic impression material

Anusavice K.J. Phillips Science of dental materials 11th edn Agar is an organic hydrophilic colloid extracted from certainSeaweed It is a sulphuric ester of a linear polymer of galactose.Though highly accurate, it has been largely replaced by alginate hydrocolloids and rubber impression material.

CompositionAgar Brush heap structure13 17 %Borates Strength0.2 - 0.5 %SulphatesGypsum hardener1.0 2.0 %Wax, hard (diatomaceous earth, clay silica, wax, rubber, similar inert powder )Filler( affect the strength / viscosity/rigidity )0.5 1.0 %Thixotropic materialsThickners0.3 0.5 %Thymol Bactericide Glycerin PlasticizerPigments & flavoursWaterReaction mediumBalance (85.5 % )Gelation process

The setting of the reversible hydrocolloid often called as gelation.It is solidification process.

The physical change from sol. to gel or vice versa is induced by the temperature change.Gel sol gel Sol gelHeating cooling 70*c 100*c 37*c 50*cGel is heated at a higher temperature liquefaction temperature ( 70*c 100*c ) to return to sol condition.It transforms to gel at temperature between 37*c 50*c ( gelation temperature ).

Gelation temperature :

Gelation temperature ---------- 37*c

It is a temperature at which sol converts into gel i. e. temperature decreases from high degree to low degree.

Gelation temperature depends on the various factors : 1. Molecular weight 2. Purity of agar 3. Ratio of agar to other ingredients

ManipulationInvolves 3 step process :Advanced preparation of the materialPreparation immediately before making the impressionMaking impressionSpecial equipmentschamber conditioning unitliquefy at 100C for 10 minute - converts gel to sol

store at 65C-68*C

Tempering section- 46*C for 3-10min

A gauze pad placed over top of the tray material.

Temper at 46*c for 3 10 min; this is done to reduce the temprature so that it can be tolerated by the sensitive oral tissues.

Making an impression Syringe material directly taken from storage compartment & applied to cavities.Prevent entrapment of air bubbles.Tray material is placed immediately in mouth to form bulk of impression.

Acceleration of gelation :By circulating cool water approx. 18*c 21*c through tray for 3 5 min. This converts sol to gel.TRAYS WATER COOLED RIM LOCK TRAYS

Removal of the impression :Necessary to remove with a jerkIndications :Widely used at present for cast duplication For full mouth impression without deep undercuts As tissue conditioner Was used for crown & bridge before the elastomers

Rubber impression materialsRubber impression materials :

In addition to the hydrocolloid gels, a group of rubber like elastic impression materials exists known as elastomers.

ADA specification No 19 identifies these materials as nonaqueous elastomeric dental impression materials. Anusavice K.J. Phillips Science of dental materials 11th edn Elastomeric material consists of a large molecules or polymers that are joined by a small amount of cross linking.

The cross linking ties the coiled polymer chains together at certain points.

To form a 3 D network referred as gel.

Chemically, there are 4 kinds of dental elastomers used as impression materials:

- Polysulfide Condensation polymerizing silicone Addition polymerizing silicone PolyetherEach type is further divided into 4 viscosity classes Light body Medium or regular body Heavy body Putty Polysulfide impression material

Polysulfide impression material :

This was the first elastomeric impression material to be introduced.

It is also known as Mercaptan or Thiokol.

Supplied as;paste in collapsible tubes as base and accelerator.Base is white colored.Accelerator is brown or greyAnusavice K.J. Phillips Science of dental materials 11th edn Chemistry and setting reaction

When the base and acceleration pastes are mixed it undergoes a chemical reaction wherby the liquid polymer sets to form a solid but highly elastic and flexible rubber like material.The lead oxide reacts with polysulfide polymer causing:Chain lengthening by oxidation of terminal SH groups.Cross linking by oxidation of the pendant SH groups

The reaction is exothermic.

Pbo2+S HS-R-SH HS-R-S-S-R-SH+H2O OR Mercaptan+leadoxide Polysulfide +water Composition :

Base Paste :Poly sulfide polymer. Filler (lithopone and TiTO2) provide strength Plasticizer dibutyl phthalate confer viscosity to paste. Sulfur 0.5% to enhance reaction. Catalyst paste Lead dioxidePlasticizer and filler are same as base paste Oleic or stearic acid act as retarders, which are added to control rate of setting. During mixing, if sufficient force is applied and spatulation performed rapidly, the material will seen thinner . This phenomenon is known as pseudoplasticity Clinical application :

There is dimensional contraction occurring during the polymerization requires use of custom made tray.

Immediate pouring of the model is indicated because water is the condensation product.

It has bad odor and tendency to flow down a patients throat promote poor patient acceptance.

Silicone Rubbers

Silicone Rubbers :These are available in two different chemical forms. They are condensation silicone and addition. Silicone materials.

Condensation silicone materials :It is a condensation reaction.Polymerization occurs as a result of cross linkage between orthoethyl silicate and the terminal hydroxy group of dimethyl siloxane to form three dimensional network.

Anusavice K.J. Phillips Science of dental materials 11th edn These reactions take place at ambient temperature thus materials are called room temperature vulcanization silicones.

Stannous octoate acts as the catalyst.

Dimethyl siloxane+orthoethyl silicate silicone rubber + ethylalcoholComposition : Supplied as a base plate and a low viscosity liquid or catalyst paste. Because the silicone polymer is a liquid, colloidal silica or microsized metal oxide is added as filler to form a paste. The influence of filler on the silicone elastomer is critical particle size within the range of 5 to 10 m. Ethyl alcohol is a byproduct of the condensation setting reaction. Its subsequent evaporation accounts for the contraction that takes placed in a set silicone rubber. To overcome large polymerization shrinkage, a high viscosity material putty was developed.

As the material has large cone of filler particles, the properties of impression material are influenced by that of the filler.

This is called as the law of mixtures.Clinical implications :Immediate pouring of the model is indicated as the libation of alcohol affects the dimensional accurately.

Hydrophobic nature of these materials after setting increases the difficulty of pouring a stone model with no surface imperfections.

Wearing latex gloves can inhibit setting of the putty as it contains sulfur.

Addition silicone or poly vinyl siloxane :

It is an addition reaction.In this base polymer is terminated with vinyl groups and is cross linked with hybrid groups activated by a platinum salt catalyst. pt salt Vinyl Siloxane+Silane Siloxane Silicone Rubber

There are no reaction by products, the hydrogen gas that evolves from the set material can result in pinpoint voids in the stone casts that are poured immediately after removing the impression from mouth.

Composition :The base paste contains poly methyl hydrogen silixane as well as other siloxane pre polymers.

The catalyst paste contains divlnyl polydimethyl siloxane and siloxane prepolymers.

Clinical implications : It is extremely hydrophpbic so care should be taken while making impression and pouring wet stone.Some manufacturers add a surfuctant to make it more hydrophillic. Sulfur contamination from natural latex gloves inhibits the setting of the addition silicone impression materials.

Most dimensionally stable and superior elastic impression materials which makes possible multiple caste from same impression.

Polyether impression materialPolyether impression material :First elastomer developed to function as impression material. It is a polyether based polymer that is cured by the reaction between aziridine rings, which are at the end of branched polyether molecules. The main chain is a copolymer of ethylene oxide and tetrahydrofuran. Cross linking and setting is brought about by an aromatic sulfornate ester cross linking is by cationic polymerization via the imine end groups .Poly ether+sulfonic ester Cross linked rubberAnusavice K.J. Phillips Science of dental materials 11th edn Composition :

Supplied as two pastes :

The base contains the polyether polymer, a colloidal silica as a filler and a plasticizer such as a glycolether or phthalate. The accelerator paste contains the alkyl aromatic sulfonate in addition to the filler and plasticizer.

Clinical implications :

They are the stiffest of the impression materials making it difficult to be removed from undercuts.

The sulfonic esters may cause skin reaction. To avoid this ,mix thoroughly before making an impression and direct skin contact should be avoided. Exhibit least amount of distortion on from the loads imposed on the set material.

Thus, multiple impressions can be poured. Stored impression are to be kept in a dry, cool environment as the material absorbs water as fluids and simultaneously leaches the water soluble plasticizer.

GYPSUM PRODUCTS

GYPSUM PRODUCTS

Gypsum products are used in dentistry for the preparation of study models for oral and maxillofacial structures and other adjuncts.

The principal constituent of dental plasters and stones is calcium sulfate hemihydrate. (CaS04)2 H2O.

Depending on the method of calcinations, two forms called - hemihydrate and hemihydrate exist.

The difference between and crystal size, surface area and degree of lattice imperfection.

Anusavice K.J. Phillips Science of dental materials 11th edn

Manufacture of dental plasterGypsum is ground and heated in open kettle at a temperature of 110 to 130 degree. The process is called as dry calcinationBeta type of crystals are formed. 110-130*c CaSO4.2H2O CaSO4.1/2 H2O Calcium sulphate Heat Beta hemihydratedihydrate

Manufacturing of dental stoneGypsum is calcined under steam pressure in an autoclave at 120-130 degree at 17 lbs /sq inch for 5-7 hrs.

120-130*c CaSO4.2H2O CaSO4.1/2 H2O Calcium sulphate Alpha hemihydratedihydrate

Type of gypsum products :

Impression plaster (Type I) composed of plaster of Paris to which modifiers have been added to regulate the setting time and setting expansion. Its rarely used because it is rigid

Model plaster (Type II) principally used to fill a dental flask

Dental stone Type III) In 1930 - -gypsum was discovered and introduced in dentistry Type III stones are preferred for casts. 4) Dental stone, high strength (type IV) Also called die stone, have high strength, hardness and minimal setting expansion. Advantage is that surface resists abrasion, where as the core of the die stone is tough and less subject to accidental breakage. 5) Dental stone, high strength, high expansion (Type V)

Have greater compressive strength than type IV dental stone. Improved strength is due to lower water : powder ratio. Higher expansion is required for the die to aid in compensating for alloy solidification shrinkageLuting materialsZINC PHOSPHATESZINC PHOSPHATES :

It is the oldest cement and it serves as a standard by which newer systems are compared.

Application Luting of restorationHigh strength basesTemporary restorationsLuting of orthodontic bands and bracketsAnusavice K.J. Phillips Science of dental materials 11th edn Composition :Powder :Zinc oxide 90% principal ingredient Magnesium oxide 10% aids in sintering Bismuth trioxide smoothens the mix Silica filler Liquid :Phosphoric acid 45-64% - reacts with zinc oxide Aluminum phosphate 2.3% buffering action Zinc phosphate 1-9% Water controls rate of reactionSetting reaction :

When powder and liquid are mixed, acid attacks and dissolves the outer layer of zinc oxide particles, releasing zinc ions into the liquid.

This is a exothermic reaction leading to formation of hydrated zinc phosphate.

In the course the pH changes to 1.6, 4 and 6 to 7 at 2min, 1 hr and 24 hrs respectively.

The set cement consists of residual zinc oxide particles (core) bound together with matrix of amorphous relatively insoluble gel of zinc, magnesium and aluminum phosphate.

Clinical implication :

Large differences in tensile and compressive strength reflects the brittle nature of the cement.

Solubility in water about 0.04% to 3.3% by weight. Because of the low initial pH, it may initiate the pulpal tissue.

Used for placing the orthodontic bands.

PropertiesCompressive strengthZinc phosphate cement is stronger than zinc oxide eugenol but not as strong as silicophosphate.

The strength of zinc phosphate cement is sufficient when used as base or luting agent.

When it is exposed to oral enviournment eg:temporary restoration its brittleness and low strength cause low it to fracture and disintegrate.

Tensile strengthThe cement is weaker in tension [5.5 Mpa] thus making it brittle.

Modulus of elasticity

It is comparatively high.This makes it stiff and resistant to elastic deformation.Solubility and disintegrationThis property is important for cements used for permanent cementation.It shows low solubility.However in mouth they show greater disintegration over a period of time.

Adhesion propertyThe retention of a cemented restoration is by mechanical interlocking of the set cement with roughness of the cavity and restoration.Biological properties

The acidity is high at the time of insertion due to phosphoric acid.Three minutes after mixing the pH 3.5.It approaches neutrality in 24 to 48 hrs.Very thin mixes should be avoided as they are more acidic.

Optical propertiesThe set cement is opaqueManipulationStainless steel spatula is used.Mixing time:1 min 15 secs

ProcedureThe powder is added in small increments.Mixing is done with stainless steel spatula using brisk circular motion.Each increment is mixed for 15 to 20 sec.A large area s covered during mixing in order to dissipate the exothermic heat.

ZINC POLYCARBOXYLATE CEMENT

ZINC POLYCARBOXYLATE CEMENT It was introduced by Smith in 1968. First dental cement developed with adhesive potential to enamel and dentin. It has desirable properties of both zinc phosphate and zinc oxide eugenol.

ApplicationPrimarily for luting permanent restorationsAs bases and linersUsed in orthodonticsfor cementation of bandsAlso in root canal filllings in endodontics

Anusavice K.J. Phillips Science of dental materials 11th edn

Composition :Powder :Zinc oxide basic ingredient Magnesium oxide 10% it aids in sinteringOr Tin oxide Bismuth salts Stannous fluoride 4.5% - increases strength, controls setting time. Pigments for shades

Liquid :

Homo polymer of acrylic acid or copolymer of acrylic with unsaturated carboxylic acids such as itaconic and maleic acid. Molecular weight of acids 22,000-50,000. Polyacid may be as freeze dried powder.

Setting reaction :

It is an acid base reaction. Reaction is between zinc oxide and polycarboxylic acid to form polycarboxylic salts.

Acid attacks powder particles which release Zn and Mg ions.

Simultaneous release of ions i.e. ionization of polycarboxylic acid takes place Then interaction between the carboxyl groups of adjacent polyacid chains and metal ions, thus crosslinked polycarboxylate salts are formed. This acts as cement matrix. The set cement consists of amorphous salt matrix in which unreacted and partially reacted Zn and Mg oxide particles are dispersed. Tightly and loosely bound water is present in set cement.

Clinical implication :

Outstanding feature of this cement is its ability to bond to enamel and dentin. Glossy appearances indicates the free carboxylic groups which bond to tooth for cement and tooth tissues. They are capable of bonding with surfaces of metallic restorations, prosthesis and appliances

ProperitesMechanical properties

Compressive strength:[55MPa]Polycarboxylate cement is inferior to zinc phosphate cement Tensile strength[6.2 Mpa]its tensile strength is slightly higher than that of zinc phosphate cement.

Solubility and disintegrationIt tends to absorb water and is slightly more soluble than zinc phosphate.

BiocompatibilityThey are less irritant than zinc phosphate cement because:The liquid is rapidly neutralized by the powder.Penetration of polyacrylic acid into the dentinal tubulesis less because of its higher molecular weight and larger size.

AdhesionPoly carboxylate cement bond chemically with the tooth structure .The carboxyl group in the polymer molecules chelate with calcium in the tooth structure.Optical propertiesThey are very opaque due to large quantity of unreacted zinc oxide.

Thermal properties They are good thermal insulators.

Mixing time:30 to 40 seconds. GLASS IONOMER CEMENTSInvented -1969 reported 1972 by WILSON AND KENTPOWDER LIQUIDpoly alkenoic acid (carboxyl containing acid)Flouroalumino silicate glassIntroductionGlass ionomer cements were introduced in 1972 ,primarily as luting agents and direct restorative material ,with unique property for bonding chemically enamel and dentin and to stainless steel and being able to release fluoride for caries protection.

It was named glass ionomer because the powder is glass and the setting reaction and adhesive bonding to tooth structure is due to ionic bond.

Glass ionomer and light cured glass ionomer cements are now used by most orthodontists for cementing bands because they are stronger than zinc phosphate and polycarboxylate cement with less demineralization at the end of treatment

The light activated resin modifid GIC are faster setting and show higher initial and sustained shear bond stength than chemically cured ones.A subset of GICs were introduced in the mid-1990s called the"Condensible" or "Viscous" GICs. These products such as Ketac Molar (3M ESPE) and Fuji IX GP (GC America), are characterized by having smaller glass particles and a higher powder-to-liquid ratio. This is said to give them higher strength, greater wear resistance, and greater flexural strength than traditional GICs.SynonymsPoly alkenoate cement

ASPA[alumino silicate polyacrylic acid]ApplicationCementation of cast alloy and porcelain restorationCementation of orthodontic bandsBonding of brackets with GIC has an advantage of avoiding acid etching ,therefore elimination of mineral loss that occur during debonding with adhesive resin.As cavity liners or bases materialAn esthetic posterior restorative As pit and fissure sealent

ClassificationType I-For lutingType II-For restorationType III-Liners and bases Type IV-Fissure sealentType V Orthodontic cementsType VI-Core build upCompositionpowder silica-41.9%Alumina-28.6%Aluminium flouride-1.6%Calcium flouride-15.7%Sodium flouride-9.3%Aluminium phosphate-3.8%

LiquidPolyacrylic acid-with iticonic ,maleic acid,etc tends to increase reactivity of the liquid,decrease viscosity and reduce tendency for gelation.Tartaric acid-improves the handling characteristics,increses working time and shortens setting time.Water-it is the most important constituent of the cement liquid ,it is the medium of reaction and it hydrates the reaction products.

Setting timeType I-4-5 minutesType II-7 minutes

PropertiesSolubility and disintegration-like silicatethe initial solubity is high due to leaching of intermediate products.

The complete setting reaction reaction takesplace in 24 hours ,so the cement should be protected from saliva in the mouth during this period .Adhesion-GIC bonds chemically to the tooth structure.

It adhere well to enamel and dentine.

Esthetically-they are inferior to silicates and composites.Biocompatibility-type II glass ionomer are relatively biocompatable.

The pulpal reaction is greater than that of ZOE cement but less than zinc phosphate cements.Anticariogenic properties-type II glass ionomer release in amounts comparable to silicate cement initally and continue to do so over an extended period of time.Proportioning and mixingPowder /liquid ratio-it is generally 3:1 by wt.Low p/l ratio reduces mechanical properties and increase the chances of cement degradation.Spatula used-agate or plastic

Manual mixing a cool dry glass slab is prefered as it allow all powder to incorporated into the mix yet maintain its plasticity.

Mixing time-45 secSetting Reaction:Leaching: when the powder and liquid are mixed together ,the acid attacks the glass particles.Thus calcium ,aluminium ,sodium and flouride ions leach out into the aqueous medium.Calcium cross links:the initial set occurs when the calcium ions cross links the polyacrylic acid chains.this forms a solid mass.Solid black particles represent unreacted glass particles surrounded by the gel{shaded structure}that form when Al+++, and Ca++ ions are leached from the glass as a result of attatch by polyacrylic acid.

The Ca++ and Al+++ ions form polysalts with the COO- group of the polyacryic acid to form a cross linked structure, the carboxyl group reacts with calcium in enamel and dentin.

-Aluminium cross links: in this aluminium also begins in cross link with polyacrylic acid chain.

Sodium and flouride ions:these ions do not take part in the cross linking some of the sodium ions in the carboxylic groups.The rest combine with flourine to form sodium flouride which is uniformly distributed within the cement.Hydration :water plays a very important role in the cement .Initially it serves as medium .later it slowely hydrates the matrix,adding to the strength of the cement.

Silica gel sheath:the unreacted glass particle is sheated with silica gel.it is formed by the ions from the outer portion of glass particle.CompositesINTRODUCTION: -If the history of all-important landmarks were to be drawn, in dentistry (or in orthodontics) BONDING would figure high in list.

Orthodontic metal bands were introduced in 1871 by W.E.Magill and have been in existence for more than 100 years..

Anusavice K.J. Phillips Science of dental materials 11th edn

The introduction of acid etching technique by Buonocore in 1955 and the development of orthodontic resins (Diglycidyl ether of Bisphenol-A, with a polyamide curing agent) by Newman in 1965, has replaced the banding with bonding, making a new era in orthodontic history.

Even since the interception of bonding to orthodontics, the materials used for bonding have undergone considerable improvement from time to time. ADHESION: -

Adhesion is a process of solid and/or liquid is interaction of one material (adhesive / adherent) with another (adherend) at a single interface. Adhesive bond strength is evaluated by debonding the system .

Most situations involving dental adhesion really involve adhesive joints. An adhesive joint is result of interaction of a layer of intermediate material (adhesive or adherent) with two surfaces (adherends).

Orthodontic bracket bonding is also an adhesive joint

TYPES OF INTERACTIONS AT INTERFACEAdhesion is classified as PHYSICAL, CHEMICAL and/or MECHANICAL bonding .

PHYSICAL BONDING involves van der Waals or other electrostatic interactions that are relatively weak.

It may be only type of bonding if surfaces are smooth & chemically dissimilarCHEMICAL BONDING involves bonds between the atoms formed across the interface from the adhesive to the adherend.

Because the materials are often dissimilar, the extent to which bonding is possible is limited & overall contribution to strength is quite low.

MECHANICAL BONDING is result of an interface that involves undercuts & other irregularities that produce interlocking of materials.

Almost every case of dental adhesion is based primarily on mechanical bonding.

Common method for surface roughness is to grind or etch the surface. Grinding gross mechanical roughness but leaves a smear layer (1-3 micron). . Composite Material:

Defined as compound of two or more distinctly different material with properties that are superior or intermediate to those of individual constituents.Composite restorative material:

Composition:

Resin matrix: High molecular weight bis-GMA or urethane di methacrylate are generally used.

Diluents like TEGDMA are used to reduce the viscosity.

.Filler Particles: Incorporation of filler particles into a resin matrix significantly improves the properties of matrix materials.

Fillers used: Colloidal silica Quartz Glass containing heavy metals like Barium,Zirconium,Strontium.Coupling agents: The bond between the two phase of composite i.e filler particles and resin matrix is provided by coupling agent.

Eg:Organo silanes like Methacryloxy propyltrimethoxy silane are most commonly used. Titanates & Zirconates.Activator initiator system: Methacrylates and di-Methacrylate monomers polymerize by the addition polymerization initiated by free radicals.

Free radicals are generated by chemical activation or by external energy activation [heat or light].Chemically Activated Resins:Contains 2 pastes 1.Benzoyl peroxide initiator 2.Tertiary amine activator [N-dimethyl-p-toluidine]

Light Activated Resin:Contain single paste 1.Photoinitiator.Eg:Camphoquinone(visible light activated) Benzoin methyl ether (uvlight activated)

2.Dimethylamino ethyl methacrylate{activator}

Initially light activated system used UV lights now visible light are used wavelength of 400-500nm (468nm)

Differences between light and chemically activated resinsLight activatedChemically activated1.Requires light of correct wavelength for activation.Activated by amine peroxide system.2.Cures only where sufficient intensity of light is received.Cures throughout its bulk3.Working time is under the control of operator.Working time is limited4.Supplied as single paste system in light tight syringes.Supplied as 2 components system5.Srinkage is towards light source.Shrinkage is towards the centre of the bulk.6.Less chance of air entrapment during manipulation.Air may get incorporated resulting in reduction of properties.7.Conturing & insertion done before initiation of polymerization.Done during polymerization.Classification: 1.Homogenous : Single size filler used. 2.Heterogenous : Filler of different size used for high filler loading

According to size Mega fill >100 Macro fill 10-100 Midi fill 1-10 Mini fill 0.1-1 Micro fill 0.01-0.1 Nano fill 50% forms monocalciumphosphate monohydrate which inhibits further dissolution.